1. Field of the Invention
The present invention relates to a pseudo-luminous panel, an optical color filter therefor, and a display element and a display device employing the pseudo-luminous panel.
2. Description of the Prior Art
FIGS. 23 and 24 show a conventional pseudo-luminous panel Q which has, for example, a square substrate 11 the main surface 2 of which is formed by an irregular or uneven reflection surface DR or UR extending in a vertical plane.
When such a conventional pseudo-luminous panel Q is disposed outdoors, for example, high above the ground G by use of a support H as shown in FIG. 25, the main surface 2 of the substrate 11 is directly irradiated over the entire area thereof by sunlight SL from above diagonally to the front of the substrate 11 in the daytime. In other word, the sunlight SL directly illuminates the main surface 2 of the substrate 11 over the entire area thereof from above diagonally to the front of the substrate 11. The sunlight SL thus falling on the main surface 2 of the substrate 11 enters thereinto. In this instance, since the main surface 2 of the substrate 11 is the irregular or uneven reflection surface DR or UR, the sunlight SL incident on such a main surface 2 irregularly enters therethrough into the substrate 11. The sunlight SL thus having irregularly entered into the substrate 11 is irregularly reflected therein. The irregularly reflected light is emitted forwardly of the pseudo-luminous panel Q through the main surface 2 of the substrate 11. In this case, the irregularly reflected light is irregularly emitted from the panel Q, since the main surface 2 is formed by the irregular or uneven reflection surface DR or UR as mentioned above. Thus, scattered light SL' derived from the sunlight SL is obtained in front of the pseudo-luminous panel Q.
The scattered light SL' results from the passage through the portion of the main surface 2 side of the substrate 11, and hence has a hue corresponding to the pass band of the main surface portion of the substrate 11 in terms of its band pass characteristic. A portion of the scattered light SL' emitted from the pseudo-luminous panel Q is directed toward the ground G. Hence, in the daytime a person M standing on the ground G diagonally below the pseudo-luminous panel Q can perceive a pattern of the main surface 2 in a color tone corresponding to the pass band of the main surface portion of the substrate 11.
When irradiating the pseudo-luminous panel Q, at night, by artificial light AL of a band covering the pass band of the main surface portion of the substrate 11 from a projector P disposed on the ground G diagonally below to the front of the panel Q, as shown in FIG. 25, the artificial light AL irregularly enters into the main surface portion of the substrate 11 through the main surface 2 and is then irregularly reflected and the irregularly reflected light is emitted as scattered light AL' from the pseudo-luminous panel Q through the main surface 2 of the substrate 11.
As is the case with the scattered light SL', the scattered light AL' also results from the passage through the main surface portion of the substrate 11, and hence has the hue corresponding to the pass band of the main surface portion of the substrate 11, and a portion of scattered light AL' is directed to the ground G. Accordingly, the person M on the ground G can perceive the pattern of the main surface 2 of the substrate 11 in a color tone corresponding to the pass band of the main surface portion of the substrate 11.
Thus, in the case where the conventional pseudo-luminous panel Q shown in FIGS. 23 and 24 is disposed outdoors, for example, high above the ground G and is irradiated by the sunlight SL in the daytime and by the artificial light AL from the projector P at night as described above, it is possible to make the person M on the ground G perceive day and night the pattern of the main surface 2 of the substrate 11 in the hue corresponding to the pass band of the main surface portion of the substrate 11.
Incidentally, the energy of the artificial light AL from the projector P is far lower than the energy of the sunlight SL owing to a limitation on the manufacture of the projector P and for some other reasons. Hence, there is a markedly large difference between the energy of the sunlight SL received by the pseudo-luminous panel Q in the daytime and the energy of the artificial light AL illuminating the panel Q at night. In the daytime the viewer M perceives the pattern of the main surface 2 of the substrate 11 by a portion of the scattered light SL' caused by irregular reflection of the sunlight SL and at night he perceives the pattern of the main surface 2 by a portion of the scattered light AL' similarly caused by irregular reflection of the artificial light AL.
On this account, the conventional pseudo-luminous panel Q depicted in FIGS. 23 and 24 is defective in that when the substrate 11 is made relatively highly reflective by a suitable selection of its material so as to permit the viewer M to distinctly recognize the pattern of the main surface 2 of the substrate 11 at night, the pattern is so dazzling in the daytime that the viewer M may sometimes be unable to perceive the pattern itself.
Moreover, when the reflectivity of the substrate 11 is made low by a suitable selection of its material so that the pattern of the main surface 2 can clearly be recognized by the viewer M in the daytime, the pattern is very dark at night and in some cases it cannot be perceived in the color tone corresponding to the pass band of the main surface portion of the substrate 11.